This is the trigger lock for Dyson V8 vacuum. I saw this model of trigger lock at our friends' place on their v15. I don't know if it's standard or aftermarket - didn't bother looking it up as I can print it! :)

The lock consists of 3 parts: bracket, piston and a cap. Just insert the piston through the holes in the bracket and cap it off. Then pull the bracket over the trigger guard - it should be a snug friction fit.

Operation is simple: push the cap to turn the vacuum on and lock the trigger. Push the other side to release the trigger.

Bracket_v1 is what I started with. It is bulkier and more robust than v2. Bracket_v2 is slimmed-down version with rounded/chamfered corners with a smaller footprint. More pleasant to touch.